This invention relates to a cross-connect apparatus for use in connecting transmission paths to one another and, in particular, to an ATM (asynchronous transfer mode) cross-connect apparatus.
Herein, it is to be noted that an ATM system serves to accomplish an ISDN (Integrated Services Digital Network) of a broadband which enables a wide variety of communication from a low speed digital signal, such as a speech data signal, to a high speed data signal, such as an image data signal carrying a moving image, by transmitting an ATM cell through a transmission path.
On the other hand, a cross-connect apparatus of the type described is similar in operation to a switch circuit included in a digital exchange but is used in a manner different from the switch circuit. More specifically, let consideration be made about an exchange system which comprises first and second exchanges connected directly to a first set of transmission paths. Under the circumstances, it is assumed that the first exchange must be also connected to a third exchange through a second set of transmission paths. In this event, the cross-connect apparatus is located among the first through the third exchanges.
In addition, such a cross-connect apparatus is also used in the case where unused transmission paths are newly used between adjacent exchanges to form semifixed routes between the adjacent exchanges.
Taking the above into consideration, the cross-connect apparatus comprises first through m-th elementary switch modules each of which is connected to a plurality of incoming or input transmission paths and a plurality of outgoing or output transmission paths, where m is a natural number. In each of the first through the m-th elementary switch modules, the incoming transmission paths are entered as first through n-th internal paths which are connected to an ATM multiplexer through an (n.times.n) ATM switch. The ATM multiplexer has a plurality of input ports equal in number to 2n and output ports, n in number. Moreover, the first through the m-th elementary switch modules are connected to one another through a connection switch module which is connected to the ATM multiplexers included in the first through the m-th elementary switch modules. Such a connection switch module also comprises first through m-th ATM switch units which are connected to the first through the m-th elementary switch modules and which may be called connection ATM switch units.
With this structure, each incoming transmission path in each of the first through the m-th elementary switch modules is not only connected directly to the outgoing transmission path of each elementary switch module but also is connected through the connection switch module to the same outgoing transmission path of each elementary switch module. This means that two routes are formed through internal paths in the conventional cross-connect apparatus, in spite of the fact that only one of the two routes is actually necessary while the remaining one of the two routes might be superfluous and may be a superfluous detour route.
In other words, each of the connection ATM switch units in the connection switch module has a superfluous capacity so as to accommodate the internal paths in the conventional cross-connect apparatus. Accordingly, the conventional cross-connect apparatus is expensive.